A motor driving control apparatus for controlling a current passing through a motor according to a current instruction inputted from an external device has to control a current passing through the motor with high precision and fast response. A motor driving control apparatus with a three-phase voltage type of PWM inverter based on the conventional technology transmits six PWM signals from an external interface potential control section to an inverter section via six photocouplers. Furthermore, there is, in order to reduce a number of insulating components, a device of a type of, not directly transmitting a PWM signal to an inverter section via a photocoupler, but coupling an external interface potential control section to an N potential control section through serial communications via a photocoupler and transmitting a PWM signal from a PWM section provided in the N potential control section to the inverter section.
FIG. 14 shows a conventional type of motor driving control apparatus with an external interface potential control section and an N potential control section coupled to each other through serial communications via a photocoupler. A motor 1 is driven by an inverter section 3 comprising switching elements such as IGBTs and transistors. A DC voltage is supplied to the inverter section 3 from a power supply via a diode module 6 and a smoothing capacitor 7. An encoder (position detector) 2 for detecting a position is connected to the motor 1.
The motor driving control apparatus is divided into an external interface potential control section A for receiving a current instruction i* from an external device and executing communications of a positional signal from the encoder 2 as well as into an N potential control section B for outputting a PWM signal to the inverter section 3. The external interface potential control section A obtains a positional signal .theta. of the motor 1 by receiving the positional signal from the encoder 2 via an encoder I/F section 18.
The current passing through the motor 1 is detected by a current detecting section 11 comprising an operational amplifier and a filter for detecting voltages at both ends of each of U-phase and V-phase detection resistors 4 and 5. The detected value of the current is transmitted to the external interface potential control section A via an insulating amplifier 8 in an insulating section C and analog-to-digital-converted by an A/D converter 14 in the external interface potential control section A.
A current control section 15 in the external interface potential control section A computes the PWM voltage instructions (Vu*, Vv*, Vw*) according to the position signal .theta., current detected values iufb, ivfb of the motor 1, as well as to the current instruction i* inputted from the external device. The PWM voltage instructions (Vu*, Vv*, Vw*) are transmitted to the N potential control section B based on serial communications between the external interface potential control section A and N potential control section B via the photocoupler 9 in the insulating section C, and a PWM signal is outputted from the PWM section 10 in the N potential control section B to the inverter section 3. An alarm signal or the like outputted from a protecting circuit 12 as information such as over-current or regeneration error in the N potential control section B is transmitted from the N potential control section B to the external interface potential control section A via the photocoupler 9 in the insulating section C with serial communications.
Each of serial communications I/F sections 13, 17 provided in the external interface potential control section A and the N potential control section B respectively has functions for transmitting/receiving data (STX) transmitted from the external interface potential control section A, a synchronizing clock for serial communications (SCLK) as a synchronization signal to the data (STX), and data (SRX) such as alarm information transmitted from the N potential control section B. The transmitting section of each of serial communications I/F sections 13, 17 converts parallel data stored in a register to serial data, and the receiving section of each of serial communications I/F sections 13, 17 periodically samples the serial data to store the data in a register respectively.
FIG. 15 shows timings in operations from current detection to output of a PWM signal in the conventional type of motor driving control apparatus with the configuration as described above. An output current from the inverter section 3 is detected, and A/D conversion of the detected current requires an A/D converting time Tad. Then, a time for preparing a PWM voltage instruction Tpwm is required to prepare PWM voltage instructions (Vu*, Vv*, Vw*) in the current control section 15 according to information for the converted values iufb, ivfb, the current instruction i* inputted from an external device, and the positional signal .theta. from the encoder 2.
FIG. 16 shows internal configuration of the current control section 15 provided in the external interface potential control section A. Herein, current control on ordinary d-q coordinate axes is described as an example, and a drawing shown in a document "Practical on Theory and designing of AC servo system--From basic to software servo--; Chapter 4, by Sugimoto et al. published by Sogo Denshi Shuppansha" is shown as a block diagram.
The current control section 15 inputs a SIN value from a SIN table 19 to a coordinate converting section 20 as well as to a coordinate reverse converting section 22 according to the position signal .theta. of the motor 1. The coordinate converting section 20 converts current feedback values iufb, ivfb detected in the current detecting section 11 from values on U-V coordinate axes to values iqfb, idfb on the d-q coordinate axes, and inputs deviation between the current instruction i* and the current feedback value iqfb on the q-axis into a PI control section 21 and also inputs deviation between zero and the current feedback value idfb on the d-axis into another PI control section 21. Each of the PI control sections 21 provides PI control as what is called a proportional-plus-integral control for the deviations, and the coordinate reverse converting section 22 reverse converts the values from the d-q coordinate axes to the U-V coordinate axes again, and outputs the PWM voltage instructions (Vu*, Vv*, Vw*). The W-phase voltage instruction Vw* is computed from the fact that a sum of three phases is zero.
The conventional type of motor driving control apparatus with the configuration as described above transmits the data from the current control section 15 to the PWM section 10 based on serial communications, so that a delay time in serial communications Tsd is required. Therefore, the conventional type of motor driving control apparatus requires a time from starting of current detection to output of PWM signals as expressed by the following equation, EQU Ttotal=Tad+Tpwm+Tsd.
Generally, when a delay time from current detection to output of PWM voltage instructions is shorter, response to a current can be enhanced. However, in the conventional type of motor driving control apparatus, serial communications are performed in order to eliminate the insulating section, therefore some delay time in serial communications is generated, so that it takes a longer time from detection of an output current till reflection thereof into the voltage instruction, namely the response can not be speeded up.
In addition, an insulating amplifier is required for current detection and an analog signal is transmitted between different potential control sections, therefore the apparatus is affected by noise due to pattern arrangement, which makes larger a packaging area to insure an insulation distance.
Since the current control section is provided in the external interface section, a high-speed serial communication system is required for providing controls with fast response, therefore response to a current is restricted in return by a serial communication speed.
Furthermore, when a plurality of motors are to be controlled, a plurality of motor driving control apparatuses as described above equivalent to the number of the motors are needed, and all of insulating sections, external interface sections and N potential control sections by a plurality of apparatuses are required even based on the serial communications. Therefore, there are problems such that a large packaging area is needed, the configuration is complicated, and the cost becomes high.